I have a late 2013 iMac on Catalina. What can I do to keep it useful?

It is called macOS because it is on a Mac, not iOS which is for iPhones.

Depends on your definition of useful and fit for purpose. What purpose, as you haven't shared that info?

If you need greater browser security, that may be achieved with current versions of Firefox or Brave browsers, since none will be forthcoming in Safari updates, and no downloadable versions of Safari are available.

If you need applications that require a newer version of macOS, then you either find suitable replacement applications still compatible with Catalina, or you will need to purchase a newer Mac capable of running the operating system that supports those application minimum requirements.

If you need a larger bootable drive, then purchase one as an external device and use cloning software to migrate from the internal drive to the external, and then change the startup drive.

If you need more RAM, that is an easy proposition for the 27-in iMac as it is user upgradeable. I purchase my RAM from OWC.

Mostly you just need a more modern Browser than Safari on Mojave, or High Sierra like Firefox or Brave.

https://brave.com/

https://www.mozilla.org/en-US/firefox/83.0/system-requirements/

Firefox 83.0 System Requirements (mozilla.org)

Opera…Thanks

https://www.opera.com/download/requirements

Opera system requirements | Opera

Thanks to dialabrain…

Firefox 115 is now the current version. runs in High Sierra.

https://www.mozilla.org/en-US/firefox/new/

Thanks to A Brody, Browsers by Mac operating system…

Browsers by Mac operating system - Apple Community

Look into the Free LibreOffice, it handles MS Office files like Word & Excel, & Page Layout…

https://www.libreoffice.org/

Thanks to Matti Haveri…

MS Office for Mac Mini - Apple Community

LibreOffice 4.0.6.2_MacOS_PPC works in OS X 10.5.8 (last official PowerPC version).

LibreOffice 4.3.7.2_MacOS_x86.dmg (and x86-64?) works in OS X 10.6.

LibreOffice 7.0.4 works in macOS 10.11 and 10.14.

https://downloadarchive.documentfoundation.org/libreoffice/old/

Thanks to Servant to Cats…

LibreOffice is up to

• Version 7.5.4 – Requires Mojave or later
• Version 7.4.7 – Requires High Sierra or later
• The LibreOffice site is now offering
• Version 7.6.2 – Requires Catalina or later
• Version 7.5.7 – Requires Mojave or later

Release notes indicate that as of August 2023, new versions of LibreOffice will likely require Catalina or later.

And thanks to VikingOSX…

Let's not overlook SoftMaker's Office 2021 suite which has familiar Word and Excel UI design, and opens these documents in their native formats.

upgrades to Mac OS high Sierra - Apple Community

FYI. Softmaker now has Office 2024 for Mac whose minimum operating system is now Catalina.

+1 re: Firefox. 👍🏽

DavidRT wrote:

What can I do to ensure my ~Mac is fit for purpose?

if it still works for the things you need it for, there is no reason to stop using it. I have an older MacBook Pro that cannot be upgraded past El Capitan. but it still works good for the things I use it for. the only adjustment I made was to install Firefox so that I can occasionally surf the net when I need portability.

👍